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| Indosinosuchus peninsularensis Lauprasert, Nilpanapan, Martin, Claude, Kamonlak Wongko, Kantanat Trakunweerayut, Dobutr, Manitkoon, Bhuttarach & Nonsrirach, 2026 |
Abstract
We describe teleosaurid remains from the Middle to Upper Jurassic Khlong Min Formation at Ban Nam Pun in southern Thailand and define Indosinosuchus peninsularensis sp. nov. This new species is diagnosed by a unique combination of cranial and postcranial features, including the nasal reaching anteriorly at the level of the 18th maxillary alveolus, absence of an incisive foramen, oval-shaped external nares, and broad ornamented osteoderms. Phylogenetic analysis positions I. peninsularensis within a polytomy alongside Mystriosaurus laurillardi and other Asian teleosaurids, supporting a monophyletic Teleosauroidea. In addition, the revision of Indosinosuchus kalasinensis as a junior synonym of I. potamosiamensis also strengthens the taxonomic framework of the genus Indosinosuchus. Indosinosuchus peninsularensis sp. nov., discovered in a low-energy lagoonal environment, offers significant insights on the ecological preferences of teleosaurids. In contrast to the fluvially deposited Phu Kradung Formation of northeastern Thailand, the lagoonal and marginal marine sediments of the Khlong Min Formation are considered indicative of a broad spectrum of habitat occupation by Asian teleosauroids. Based on these observations, a high degree of ecological plasticity has been inferred for Thai teleosaurids, and their extensive dispersal across both the Sibumasu and Indochina terranes during the Middle to Late Jurassic has been further substantiated. The recognition of I. peninsularensis sp. nov. contributes to our understanding of teleosaurid diversity and paleobiogeography in Southeast Asia.
Keywords: Indosinosuchus, Khlong Min Formation, Sibumasu, Phu Kradung Formation, Indochina
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| Indosinosuchus peninsularensis sp. nov. from the Khong Min Formation, Ban Nam Pun, southern Thailand. Photographs and interpretive drawings of Indosinosuchus peninsularensis sp. nov. from the Khong Min Formation, Ban Nam Pun, Nakhon Si Thammarat Province, southern Thailand. PRC-205: anterior rostrum in dorsal view (A, B) and dorsal vertebrae in ventral view (C, D). PRC-206: osteoderms and dorsal vertebrae in dorsal view (E, F) and ventral view (G, H). Abbreviations: dv, dorsal vertebrae; en, external nares; mx, maxilla; n, nasal; ost, osteoderm; pmx, premaxilla. |
CROCODYLOMORPHA Hay, 1930
THALATTOSUCHIA Fraas, 1901
NEOTHALATTOSUCHIA Young et al., 2024a; Young et al., 2024b
TELEOSAUROIDEA Delfino & Dal Sasso, 2006
TELEOSAURIDAE Geoffroy Saint-Hilaire, 1831
Genus Indosinosuchus Martin et al., 2019
Indosinosuchus peninsularensis
Holotype: PRC 205 and PRC 206, comprising an anterior portion of the rostrum, osteoderms, and dorsal vertebrae.
Type locality: Ban Nam Pun, Bang Khan District, Nakhon Si Thammarat Province, southern Thailand.
Stratigraphic occurrence: Lower part of the Khlong Min Formation, Thung Yai Group, late Middle Jurassic to early Late Jurassic.
Diagnosis. Indosinosuchus peninsularensis, PRC 205, is characterized by the following combination of characters (autapomorphies denoted with*): (1) four premaxillary alveoli; (2) moderately laterally expanded premaxilla with subequal length and width, producing a broad yet unflared outline; (3) margin of premaxillary-maxillary suture is concave between the 4th premaxillary –1st maxillary alveoli; (4) the external narial opening is subcircular or slightly ‘8-shaped’ in dorsal view; (5) absence of incisive foramen at medial contact of premaxillae*; (6) anterior tip of nasals reaching the level of the 18th maxillary alveolus*.
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| Locality, lithostratigraphy, and petrographic characteristics of the fossiliferous limestone within the Khlong Min Formation at Ban Nam Pun, southern Thailand. (A) Tectonic subdivision map of Thailand (modified after Udchachon et al., 2022), illustrating the distribution of Jurassic sedimentary rock units (based on Meesook & Saengsrichan, 2011). The Khlong Min Formation, including the Ban Nam Pun locality, is situated within the Sibumasu Terrane, whereas the Phu Kradung Formation and its equivalents are located within the Indochina and Sukhothai Terranes. (B) Simplified geological map of the Krabi–Khlong Thom–Trang region (adapted from Thailand Department of Mineral Resources, 1999; Meesook & Saengsrichan, 2011), with the study site marked by a red star. (C) Field photograph of the fossiliferous limestone outcrop intercalated with mudstone. The rock hammer (circled) is 30 cm in length for scale. (D–F) Close-up view of fossiliferous limestone rich in bivalves, (D) Modiolus sp. assemblage, (E) Actinostreon sp. (F) Protocardia sp. (G) MF1: Bioclast wackestone characterized by shell fragments, benthic foraminifera (f), and peloids (p). The yellow arrow indicates a bivalve shell with geopetal fabric: the lower portion infilled with micritic matrix and peloids, and the upper portion filled with sparry calcite cement. (H) MF2: Bioclast-peloidal packstone to grainstone, dominated by peloids (p) and benthic foraminifers (f) with minor ostracod shells (o). |
Komsorn Lauprasert, Apirut Nilpanapan, Jeremy E. Martin, Julien Claude, Kamonlak Wongko, Kantanat Trakunweerayut, Nuntida Dobutr, Sita Manitkoon, Supanut Bhuttarach and Thanit Nonsrirach. 2026. A new teleosaurid (Crocodylomorpha, Thalattosuchia) from the Sibumasu Terrane of Southeast Asia and A Taxonomic Reassessment of Indosinosuchus. PeerJ. 14:e20944. DOI: doi.org/10.7717/peerj.20944 [2026-03-20]
